Assistant U.S. Attorney Thomas Wales is believed to be the only federal prosecutor to die in the line of duty, although authorities have not established a motive in the 2001 slaying.

"We will never give up our search for the truth," said Holder, who came to Seattle to reassure friends and family of his former colleague that the investigation remained active, even after 10 years.

He emphasized that new information was coming in on a regular basis. But law enforcement officials believe witnesses who hold the key to solving the crime possibly are too afraid to come forward.

Wales was 49 when he was killed on the night of Oct. 11, 2001, as he sat at his computer in the home in the Queen Anne neighborhood. The shots went through a window from his backyard.

The longtime federal prosecutor mostly handled white-collar crimes and had been active in a gun-control group.

His son, Tom Wales, told The Associated Press that anniversaries, like this 10th one, are for the public. They remember their dad every day, especially at happy times such as his sister's wedding earlier this month, he said.

"We're patient," he said, a reference to the time that has passed since his father's death. "We know this kind of complicated investigation can take a very long time indeed."

"Things have been progressing every year," added Amy Wales, his sister.

In a video created for the case and in their comments to the media, both children said Wales was respected in his community and at his job, but he was primarily a great father.

Amy Wales urged witnesses to be brave and make an effort for justice, just as her father did during his career.

Tom Wales compared his father to the character Jimmy Stewart played in "It's a Wonderful Life," and talked about the ways he affected other people's lives, from planting trees on the top of Queen Anne hill to climbing mountains with his children.

For a time, police and FBI focused on an airline pilot who was bitter over being prosecuted by Wales in a case involving the sale of helicopter parts. His home in the Seattle suburb of Bellevue was searched three times, but he was not charged.

A Bellevue gun dealer also was arrested as a material witness in the case because he had purchased parts for a handgun like the one used to kill Wales. A unique gun barrel had been used in the shooting.

The gun dealer was convicted in 2007, but the conviction was overturned in 2009.

Wales' killing remained a top priority of the FBI, said Gregory Fowler, the head of the bureau's office in Portland. The Justice Department has offered a $1 million reward for information leading to a conviction of the shooter.

"We know there are people out there who haven't come forward," Fowler said. "Even the smallest clue may help."